Air Filter Sizes — HVAC, Furnace & AC Filters for Home & Business
Find your exact HVAC, furnace, or air conditioner filter size fast. We stock hundreds of standard sizes in 1″, 2″, 3″, 4″, 4½″, 5″, and 6″ depths — plus made-to-spec filters in ⅛″ increments. Every filter ships with our Filter Fit Guarantee™, and every size is available for both home and business use.
Search by Exact Filter Size
Know your exact dimensions? Use the builder below. Supports ⅛″ increments.
Odd size not in stock as a standard? → Order a custom-built filter in any dimension.
Most Popular Air Filter Sizes
These eight sizes cover the majority of systems we ship. Click your size to shop all available filter types, MERV ratings, and depths.
Don't See Your Size?
We build filters to your exact dimensions in ⅛″ increments — no size is too odd.
Build a Custom Filter →Browse All Air Filter Sizes by Depth
1″ Filters
Standard depth for most furnaces and return grilles. Replace every 1–3 months.
2″ Filters
Higher dust capacity and longer service life than 1″. Common in both home and business systems.
4″ & Deeper Filters
Includes 3″, 4″, 4½″, 5″, and 6″ depths. Extended service life (6–12 months), lower static pressure, and higher dust capacity.
How to Measure Your Air Filter
Finding your filter size takes about 30 seconds. There are three reliable methods:
1. Read the Old Filter
Pull your current filter and check the printed size on the frame (e.g., 16x25x1). This is the nominal size — order by this number.
2. Measure the Slot
Measure Length × Width × Depth of the filter slot. Round up to the nearest whole inch. A 15¾″ × 24¾″ × ¾″ slot takes a 16x25x1.
3. Order Odd Sizes
If your filter isn't a standard size, measure to the nearest ⅛″ and order a custom filter. Built to your exact specs.
→ Full measuring guide with photos
Which Filter Depth Should I Choose?
Depth is the third number in the size (the 1, 2, or 4 in 16x25x1). It's dictated by your HVAC equipment — check your system or the filter you're replacing before switching depths.
| Depth | Typical Use | Replace Every |
|---|---|---|
| 1″ | Most furnaces, air handlers, and return grilles | 1–3 months |
| 2″ | Rooftop units and systems with deeper slots | 2–3 months |
| 4″ | Media filter cabinets with higher dust capacity | 6–12 months |
| 4½″ / 5″ | Aprilaire, Honeywell, Lennox, Trane media cabinets | 6–12 months |
| 6″ | High-capacity media cabinets and specialty systems | 6–12 months |
Air Filter Size FAQs
What are the most common HVAC filter sizes?
The most common 1″ furnace filter sizes are 16x25x1, 20x25x1, 16x20x1, 20x20x1, and 14x25x1. For 2″, the most common is 20x20x2. For deeper media cabinets, 16x25x4 and 20x25x4 are the most widely used. We stock all of these plus hundreds more for home and business HVAC systems.
What does the third number in a filter size mean?
The third number is the filter's depth (thickness). A 16x25x1 filter is 16 inches wide, 25 inches long, and 1 inch thick. Depth is determined by your HVAC equipment — a 1″ filter will not fit a slot designed for a 4″ filter, and forcing a thicker filter into a shallow slot can damage the frame or block airflow.
What is the difference between nominal and actual filter size?
Nominal size is the rounded size printed on the filter (e.g., 16x25x1). Actual size is the true physical dimension, typically ¼″ to ½″ smaller so the filter slides in and out of the slot easily. Always order by nominal size unless you need a made-to-spec custom filter.
My filter size isn't listed. Can you build a custom size?
Yes. We build custom filters to your exact dimensions in ⅛″ increments. Measure your filter slot to the nearest ⅛″ and order through our Custom Filters collection. Most custom orders ship in 5–7 business days.
Can I use a 2″ filter where a 1″ fits?
Only if your filter slot is physically deep enough. Forcing a thicker filter into a shallow slot can damage the frame, allow air bypass around the filter, or block the blower compartment. Always match the depth your system was designed for.
Do you carry commercial and bulk sizes?
Yes. We stock hundreds of sizes suited for rooftop units, air handlers, and large-format equipment — including 20x20x2, 24x24x2, 20x20x4, 24x24x4, and larger. For volume pricing, request a quote and our team will respond within one business day.
How often should I replace my air filter?
Replacement intervals depend on depth and MERV rating. 1″ filters typically last 1–3 months, 2″ filters 2–3 months, and 4″ or deeper media filters 6–12 months. Homes and facilities with pets, wildfire smoke exposure, or higher occupancy should replace more often.
What MERV rating should I choose?
MERV 8 is a solid baseline for equipment protection. MERV 10–11 adds meaningful dust and pollen capture without a major pressure drop. MERV 13 captures the smallest particles your system can reasonably handle. Always confirm your equipment's maximum supported MERV before upgrading. See our MERV guide for details.
Are furnace filters and AC filters the same thing?
For forced-air systems, yes. The same filter typically serves both the furnace and the air conditioner because both use the same blower and return ductwork. "Furnace filter," "AC filter," "air handler filter," and "HVAC filter" refer to the same product in almost all residential and light-commercial systems.
Do you offer filters for both homes and businesses?
Yes. Every size and depth on this page is available for both residential and commercial use. We ship to homeowners, property managers, facility managers, contractors, and purchasing teams nationwide, with the same Filter Fit Guarantee on every order.
Finding the Right Replacement Air Filter Size
Replacement air filter sizes for HVAC, furnace, and air conditioner systems follow a standard format: width × length × depth, measured in inches. Whether you're replacing a filter in a central air conditioner, gas or electric furnace, heat pump, air handler, or rooftop unit, the size printed on your current filter is the number you'll order by. RememberTheFilter.com stocks the full catalog of standard filter sizes — from compact 8x14x1 up through large-format 30x36x2 — and builds custom filters in ⅛″ increments for equipment that doesn't use a standard size.
Furnace Filter Sizes
Furnace filters sit inside the blower compartment or in a dedicated return-air filter slot. The most common furnace filter sizes are 1″ deep and fit standard return grilles — sizes like 16x25x1, 20x25x1, 16x20x1, and 20x20x1. High-efficiency furnaces with built-in media cabinets use deeper 4″ or 5″ filters like 16x25x4, 20x25x4, and 20x25x5, which last 6–12 months between replacements.
Air Conditioner Filter Sizes
Central air conditioner filters are physically the same filters used by furnaces in forced-air systems. The AC coil, blower, and return ductwork all pull through the same filter, so the size you use in summer is the size you use in winter. If you have a split system or a heat pump, the filter typically sits in the return grille or at the air handler — common AC filter sizes include 14x25x1, 16x25x1, 20x25x1, and 20x20x1.
HVAC Filter Sizes for Commercial Buildings
Commercial HVAC systems — rooftop units, packaged units, air handlers serving offices, schools, retail, warehouses, and healthcare facilities — use larger or thicker filters to handle higher airflow volumes. Common commercial sizes include 20x20x2, 24x24x2, 20x20x4, and 24x24x4. We also carry extended-surface bag filters, rigid cell filters, and HEPA filters for demanding filtration applications. Facility managers and contractors can request a quote for bulk pricing and ongoing supply contracts.
Media Cabinet Filter Sizes
If your system uses a whole-home media filter cabinet — often branded Aprilaire, Honeywell, Lennox, Trane, Carrier, Bryant, or Goodman — you'll need a 4″, 4½″, or 5″ deep filter. These are the most common whole-home filter cabinet sizes we ship:
- 16x25x4 — fits many Aprilaire and Honeywell cabinets
- 20x25x4 — fits many Lennox and Trane cabinets
- 16x25x5 — fits Aprilaire 201 / 2200 / 2400 cabinets
- 20x25x5 — fits Aprilaire 213 / 413 and Space-Gard cabinets
- 16x20x5 — fits Lennox Healthy Climate cabinets
Always verify against the filter currently in your cabinet or your equipment's filter specification before ordering.
Why Filter Size Matters
Installing the wrong size air filter is one of the most common causes of poor HVAC performance. An undersized filter leaves gaps where unfiltered air bypasses the filter, sending dust directly into the blower and evaporator coil. An oversized filter bends or crushes in the slot, restricting airflow and raising static pressure. Either mistake shortens equipment life and drives up energy costs. Ordering by nominal size — the number printed on the filter frame — ensures a proper fit every time.
Shop by Filter Type
Once you know your size, you can shop by filter type and efficiency:
Shop by MERV Rating
Match your efficiency to your system's capability:
Shop by Brand
We carry trusted manufacturers alongside our own PrimeShield house brand:
Need Help Finding Your Size?
Our team answers filter questions every day. Text, call, or email — we'll help you identify the right size and filter type.
Contact Our Filter Team →